The purpose of this application is to obtain a pulsed laser system in order to complete the establishment of the Time-Resolved Biophysical Spectroscopy Laboratory in the Department of Biochemistry. This laser will act as the light source for time-resolved optical experiments from the psec to msec time ranges, providing experimental capabilities unmatched in any other biophysics laboratory. The laser will greatly improve the time resolution, tunability, and rate of data collection, greatly increasing the utility of this laboratory as a shared resource in the University of Minnesota Medical School. When pulsed in the psec time range, this laser will provide the light source for measurements of fluoroscence and fluorescence anisotropy decay, in the range of hundreds of psec to hundreds of nsec. When the laser is pulsed in the 50 nsec time range, we will probe phosphorescence and phosphorescence anisotropy. These measurements will provide quantitative information about the separation distances and motions (both translational and rotational) of both intrinsic biological chromophores and extrinsic probes. The principal biophysical problems to be investigated will be (1) the structure of photoreceptor membranes, (2) the dynamics of biological membranes, particularly enzymes in sarcoplasmic reticulum and mitochondria, (3) the molecular mechanism of muscle contraction, (4) the structure and dynamics of Alpha2-macroglobulin, (5) the structure of metalloproteins, (6) molecular motion in lipid-peptide complexes, (7) subnanosecond and nanosecond biomacromolecular motions, (8) the molecular dynamics of lymphocyte plasma membranes, as affected by mitogens and by diabetes, and (9) interaction of prothrombin with membranes.